Bleaching process for cotton of low grade for color



Sept. 6, 1955 s. A. SIMON ET AL 2,717,193

BLEACHING PROCESS FOR COTTON OF LOW GRADE FOR COLOR Filed Nov. 19, 1952 2 sheets-sheet 1 Sept' 6, 1955 s. A. s|MoN ETAL 2,717,193

BLEACHING PROCESS FORCOTTON OF LOW GRADE FOR COLOR Filed Nov. 19u annua() nu 2 Sheets-Sheet 2 se e? @w e Y #@1122 wrap/27910 va/v was 71%/ f? ATTORNE United States Patent O BLEACHING PROCESS FOR COTTON OF LOW GRADE FOR COLOR Simon A. Simon, Longmeadow, and Harvey Clayton Ruhf, Springfield, Mass., assignors to Chicopee Manufacturing Corporation, a corporation of Massachusetts Application November 19, 1952, Serial No. 321,378

14 Claims. (Cl. 8-111) This invention relates to the bleaching of cotton, either woven or nonwoven, and more particularly relates to an improved process for the bleaching of cotton of low grade for color, although the invention has application to the bleaching of higher grades of cotton.

It has long been recognized in the textile industry that there is a problem associated with the bleaching of cotton of low grade for color; also variously referred to as denitely shaded cotton, blue cotton, discolored cotton, light gray cotton, gray cotton, dull cotton, off-cotton and oishades of cotton; not encountered in the bleaching of the better grades of cotton which are called white or unshaded cotton. The desire has beenv repeatedly expressed in textile publications for a solution to the problem of bleaching cottons of low grade for `color because of the many ditculties the use of such cottons presents. If discolored cottons having bers that are but slightly oit-shade are blended with higher grade cottons,y woven into piece goods and bleached, the departure from white is so marked that no amount of bluing or tinting will change the apparent elect and any attempt made to hide the shading will result in a saddening of the natural brilliancy of the cotton. It is customary practice in the textile industry to avoid carefully the blending of discolored cottons with the whiter shades because the bleacher cannot whiten the blended cottons with any degree of economy and resultant strength of the bers. Although the factors involved and responsible for the discoloration of cotton are known, it is recognized in the textile industry that no practical method of bleaching discolored cotton to the degree of whiteness associated with the bleaching of white cotton has been suggested or is known, even though a great amount of work has been done to develop a method for the satisfactory bleaching of such cotton.

A substantial amount of cotton is discolored and classed as dull or gray because the bers have been subjected to the action of microorganisms having the ability to grow and multiply on the surface of fibers as well as to penetrate the bers and multiply in the lumina. Many of the microorganisms are dark in color and their presence as discolored matter on the surfaceand in the lumina gives the bers a dull or grayed appearance.

The cotton ber shown in cross-section and magnication in Figure 1 is a typical ber consisting of a characteristic flattened, twisted, irregular tube of cellulose 10, and a wall 12 surrounding a hollow space 14 called a lumen and shows microorganisms 16 growing on the outside of the wall of the ber. Figure 1 also shows punctures 18 in the ber wall and organisms 20 growing in the lumen of the ber. Fibers in which there is growth of microorganisms in the lumina are duller and of lower grade for color and are least responsive to bleaching by conventional methods. Fibers n which the microorganisms have penetrated the cell wall and are present in the lumina do not respond satisfactorily to conventional methods of bleaching and do not provide bleached material having a degree of whiteness suitable for use in the manufacture of white cotton and white goods. Discolored cotton of this type 2,717,193 Patented Sept. 6, 1955 may be bleached to a satisfactory whiteness by subjecting it to a series of conventional bleaching cycles, but this results in a degradation of the cellulose molecules making up the bers to such an extent that the cotton cannot be satisfactorily used in conventional textile processes. Fabrics woven from this type of discolored cotton and subsequently bleached by repeated conventional bleaching operations do not have satisfactory laundering and wearing properties. Repeated bleaching of cotton results in damage to the bers and markedly increases ber fragility. Cotton having markedly increased ber fragility is not acceptable for surgical uses because of the excessive amount of y and ber dust associated therewith.

It is an object of this invention to provide a process for the bleaching of cotton in general and cotton of low grade for color in particular, either in the form of bers or fabric, to a satisfactory degree of whiteness without serious damage to the bers and increase in ber fragility.

Itis another object of this invention to provide a process for the bleaching of discolored cotton, having discolored matter within the lumina of the bers due to the action of microorganisms, to a satisfactory whiteness without serious damage to the bers.

It is another and further object of this invention to provide a process by which cotton of low grade for color having a percent reflectance approximately within the range of from 64 Rd to 72 Rd is bleaced in a single bleaching operation in batch or continuous method to a percent reflectance of not substantially less than 88.5 Rd.

The objects of are accomplished by a bleaching process in which cotton bers or cotton textiles remain in a substantially inactive bleaching bath containing a per compound as a bleaching agent, at a temperature of the bleaching bath below the temperature at which the bleaching agent is activated and rapidly decomposed, for a latent period of time such that the bleaching agent is able to penetrate into the lumina of the bers which contain discolored matter in the lumina. During the latent period, decomposition of the bleaching agent proceeds at a slow rate but a substantial amount remains undecomposed. At the end of the latent period, the bleaching solution is activated and bleaching of the cotton continues until the discolored matter responsible for discoloring the bers is bleached and the bleaching agent is exhausted.

In the drawings:

Figure 1 is a greatly magnied perspective in cross-section of a cotton ber discolored by the action of microorganisms;

Figure 2 is a graph in which the percent reflectance of bleached cotton in Rd units is plotted against the percent of the hydrogen peroxide in the bleaching bath which is decomposed during the latent period and the curves in this graph show the relation between the time and temperature of the latent period to the percent reflectance in Rd units of bleached cotton as well as their relationship to the amount of bleaching agent decomposed during the latent period;

Figure 3 is a graph in which the percent reflectance of bleached cotton in Rd units is plotted against the time of the latent period and shows the relationship between the temperature of the bleaching solution during the latent period, the duration of the latent period and the percent reilectance of the bleached cotton.

The period of time during which the material to be bleached is kept in an inactive bleaching solution containing a per compound is at least about one and onequarter hours but may be as long as twenty-four hours. If the time is substantially less than one and one-quarter hours, cotton bers or woven materials, made from discolored bers, and particularly made from bers in which discolored material is present in the lumina of the bers,

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will not be bleached to a satisfactory whiteness. The time of the latent period may be considerably longer than one and one-quarter hours and even as long as -twentyfour hours without any deleterious effect upon the fibers. The required time of the latent period is the shortest at a temperature of the bleaching bath of 50 C.; however, if the temperature of the bleaching bath is C. or lower, the time of the steeping period must be at least about one and one-half hours. The time of the steeping period must also be at least about one and one-half hours if the temperature of the steeping bath is 55 C.

leaching agen s satisfactory for use in the practice of this invention are generally referred to in the bleaching art as per compounds, and are compounds capable of releasing oxygen on activation. Aqueous solutions of hydrogen peroxide and sodium peroxide or per compounds which behave in solution as peroxides, such as sodium perborate and other inorganic perborate salts, are suitable for use in the bleaching process of this invention. Per compounds, when used as bleaching agents, may be conveniently maintained in a latent state, in which there is a minimum amount of decomposition and consequent exhaustion of their bleaching ability by the evolution of oxygen, by the presence in the bleaching solution of a substance such as sodium silicate which lends stability to the bleaching solution and is known as an assistant. A bleaching solution, which has been maintained in an inactive state in the presence of assistants, may be activated by raising the temperature to a critical degree, by the addition of ctivator such as sodium carbonate and sodium hydroxide, or By raising the pH to about 12 or higher. The critical temperature and pH of such a bleaching solution varies with the per compound used and with the amount and kind of assistants present in the solution.

The whiteness of cotton in fiber or textile form is conventionally measured by means of an instrument known as the Hunter Color and Color Difference Meter, which measures diffused reflectance. Measurements of whiteness made by this method are called percent reectance and are expressed in Rd units.

Chemical degradation of cotton is determined according to A. S. T. M. designation D539-40T. This method measures the fluidity of solutions of cotton and the measurements are expressed in rhes.

Reectance, as measured according to the Hunter Color and Color Difference Meter, is uniform for cotton fibers, but varies with the number of threads per inch when reliectance measurements are made on cotton fabrics. A fabric having a lesser number of threads per inch will be lower in measured percent reflectance than a fabric having a greater number of threads per inch.

Unbleached or raw cotton is considered to be white or normal if it has a percent retiectance of 72 Rd or above` Cottons classed as dull have a percent reflectance of 64 Rd to 72 Rd. Cottons classed as gray have a percent refiectance of less than 64 Rd. A fabric is considered to have unsatisfactory laundering and wearing properties if the fibers have a fluidity of greater than l0 rhes. Cotton fibers having a percent reflectance of 88.5 Rd and above are referred to as white and cotton of this degree of whiteness is used by the medical and dental professions and in the home as such or in various forms such as pads, rolls and balls.

Cotton fibers can be prepared for bleaching according to the process of our invention by any of a variety of preliminary steps commonly practiced in preparing cotton fibers for conventional bleaching operations. A typical series of preparatory steps includes wet-out and desizing, washing, souring, washing, scouring and washing.

The following examples are given to illustrate the various modifications of the invention and to demonstrate the limits of the invention, but it is to be understood that they are presented only by way of illustration and that the invention is not to be restricted or limited thereby,

4 l Example I Ten-gram portions of kier-boiled cotton having a fluidity of 4 rhes and a percent reflectance in the raw state of 68 Rd were each immersed in 100 cc. of an aqueous bleaching solution containing 0.28 g. of hydrogen peroxide, 0.10 g. of sodium carbonate, and 0.10 g. of sodium silicate. Eight series of beakers, with eight beakers in a series, containing a cotton portion and bleaching solution were maintained each at a separate temperature for a latent period varying in length. The temperatures were 5 C., 15 C., 25 C., 40 C., 45 C., 50 C., 55 C., and 60 C. At each individual temperature the bleaching solution was immediately raised to a temperature of about 85 C. after fifteen minutes, thirty minutes, one and onequarter, one and one-half, two, two and one-half, three, and twenty-four hours immersion of the cotton in the bleaching solution. In all instances, after elevation of the temperature to 85 C., the solutions were held at that temperature until the bleaching agent was exhausted which required about two hours. The cotton samples were then removed from the bleaching solution and washed until clean and dried. The percent reflectance of each dried cotton sample was measured and the percent decomposition of the hydrogen peroxide during the steeping period was determined. Fluidities of all samples of bleached cotton were determined and were found to be between 4.5 and 5.5 rhes.

The results of the determination of the percent of the hydrogen peroxide in the bleaching bath decomposed at the eight different temperatures at which the cotton samples were immersed in the bleaching solution during latent periods of one, one and one-quarter, one and one-half, and two hours are given in the graph of Figure 2 as points on the curves. The results of determinations of percent reflectance in Rd units for cotton samples immersed in an inactive bleaching solution for all durations of the latent periods and at temperatures of 15 C., 25 C., 40 C., 45 C., 50 C., 55 C., and 60 C. are given in the graph of Figure 2 as points on the curves.

Figure 3 in particular shows in graphic form the relationship between the time of the latent period and the temperature of the bleaching solution during the latent period and the effect of these two conditions on the percent reflectance of the bleached cotton. It is apparent from an examination of Figure 3 that to obtain bleached cotton with a percent reliectance of 88.5 Rd, it is necessary that the material to be bleached remain in the steeping bath in an inactivated state for at least about one and one-quarter hours and that the time may only be this short if the temperature of the bleaching solution is C. The results graphically shown in Figure 3 also show that if the temperature of the bleaching solution is below 50 C., the steeping time may be as short as one and onehalf hours and that bleaching to a percent refiectance of 88.5 Rd is not accomplished when the temperature of the bleaching solution is substantially greater than about C. It is preferred that the temperature of the bleaching solution be not substantially below 15 C. during the latent period, although discolored cotton may be bleached to a percent reflectance of 88.5 Rd at a temperature of the bleaching solution substantially below 15 C. when the time of the latent period is at least about one and onehalf hours.

The graph of Figure 2 shows the relationship between the percent of the per compound, in this case hydrogen peroxide, which is decomposed during the latent period and the conditions of time and temperature to which the material to be bleached is subjected in the bleaching solution during the latent period and the effect of these conditions on the percent refiectance of the bleached cotton. The results presented graphically in Figure 2 show that if more than about 26 percent of the hydrogen peroxide is decomposed during a latent period of two hours, the cotton is not bleached to a percent reectance of 88.5 Rd.

Example II Ten gram portions of kier-boiled cotton having a uidity of 4 rhes and a percent reflectance in the raw state of 68 Rd were each immersed in 100 cc. of an aqueous bleaching solution containing 0.8 g. of odium perborate, 0.1 g. sodium carbonate and 0.1 glsmtmslicate. wo beakers containing the cotton and bleaching solution were maintained at 25 C., one for one hour and the other for two hours, and then immediately raised to a temperature of about 85 C., at which temperature the bleaching agent was activated and active bleaching occurred. The temperature was held at 85 C. until the bleaching agent was exhausted. The cotton samples were removed from the exhausted bleaching solution, washed until clean and dried.

An additional two beakers containing the cotton and bleaching solution were maintained at a temperature of 50 C., one for a latent period of one hour, and the other two hours. After the latent period, the bleaching agent was activated by elevation of the temperature of the bleaching solution to 85 C. and bleaching of the cotton samples was finished as above.

The percent reflectance of each dried cotton sample was measured. Fluidities of all samples of bleached cotton were determined and were all found to be below 5 rhes. The results of this experiment are given in the table below in which percent reflectance is expressed in Rd units:

Example III A ten-gram portion of kier-boiled cotton having a uidity of 3 rhes and a percent reflectance in the raw state of 68 Rd was bleached according to the bleaching procedure of Example I. The time of the latent period was two hours and the temperature of the bleaching solution during the latent period was 25 C. After the latent period, the temperature was immediately raised to 85 C. and held at that temperature until the bleaching agent was exhausted, which required about two hours. The cotton sample was then removed from the bleachingsolution and washed until clean and dried. The uidity of the bleached cotton sample was 4.6 rhes. The same sample of cotton was again subjected to bleaching according to the same conditions as in the rst bleaching. The twice bleached cotton had a fluidity of 8 rhes. After a third and fourth bleaching under the same cinditions, the uidity of the cotton samples was 12 and 18 rhes, respectively.

Example IV one portion of fabric was immersed Was held at 20 C.

for a latent period of two hours and then rapidly elevated to 85 C. and maintained at that temperature for two hours. The bleaching agent was exhausted after two hours at 85 C. and the farbic was removed from the bleaching solution, washed and dried. The bleached fabric had a percent reectance of 89.0 Rd and a fluidity of 4.5 rhes. The temperature of the bleaching solution in which the other portion of fabric was immersed was rapidly brought up to 85 C., immediately after immersion of the fabric in the bleaching solution. The temperature of the bleaching solution was maintained at 85 C. for two hours at which time the bleaching agent was exhausted. The fabric was removed from the bleaching solution, washed, and dried, and had a percent reectance of 80.0 Rd and a fluidity of 4.7 rhes.

A 28 x 24 cotton fabric is not considered white enough for surgical and household uses unless it has a percent 5 reflectance of at least 83 Rd.

The results of the experiments show that cotton fibers having a percent reflectance in the raw state as low as 68 Rd may be satisfactorily bleached by a single bleaching operation in which no additional bleaching agent is added to the bleaching solution at the end of the latent period.

The bleaching process of our invention may be operated continuously. One method of continuous operation is to use a J-box of the type having a capacity such that the fabric remains in the J-box for from at least one and one-quarter hours to as long as two or more hours. The temperature of the solution and fabric in the J-box can be varied and the fabric may be removed from the J-box at such a rate that the time of the latent period may be substantially greater than one and one-quarter or one and one-half hours. When operating the bleaching process of this invention in a continuous manner, the same conditions and limitations apply as those found necessary and advantageous in batch bleaching operations.

Although our bleaching operation is particularly aplicable to the bleaching of cottons of low grade for color it may also be practiced in the bleaching of white or unshaded cottons and results by a single bleaching operation in an improvement in the percent reflectance of such cottons and a degree of whiteness not obtainable by a conventional single bleaching operation.,-

This application is a continuation-in-part of our U. S. patent applications, Serial Numbers 199,468 and 199,469, tiled December 6, 1950.

What is claimed is:

1. The method of bleaching cotton of low grade for color to a per cent reiectance of at least 88.5 Rd comprising the steps of: immersing the cotton in an inactive alkaline bleaching solution of a per compound for a minimum period of time of at least 11A to 11/2 hours, maintaining the temperature during a said period of time of at least 11A hours not substantially above 50 C., and during a said period of time of at least 11/2 hours not substantially above 55 C.; the amount of decomposition of the per compound while the cotton is immersed in the inactive alkaline bleaching solution for a period of time of not longer than about two hours being not greater than about twenty-six per cent; eleyating the temperature of the bleaching solution to a out 85 C., hereby the Y /bgghjngsplprvitgdg and mairxlxiiin'ghe D0 b eaching solution 1n an ac d state until the per compound is substantially completely exhausted.

2. A method according to claim l in which the per compound is hydrogen peroxide.

3. A method according to claim 1 in which the per compound is sodium perborate.

4. The method of bleaching cotton of low grade for color; due to the presence of discolored matter within the lumina of the iibers, to a per cent rellectance of at least 88.5 Rd comprising the steps of immersing the cotton in an inactive alkaline bleaching solution of a per compound for a minimum period of time of at least 11/4 to 11/2 hours, maintaining the temperature during a said period of time of at least 11A hours not substantially above 50 C., and during a said period of time of at least 11/2 hours not substantially above 55 C.; the amount of decomposition of the per compound while the cotton is immersed in the inactive alkaline bleaching solution for a period of time of not longer than about two hours being not greater than about twenty-six per cent; elevating the temperature of the bleaching solution to about 85 C., whereby the bleaching solution is activated; and maintaining the bleaching solution in an activated state until the per compound is substantially completely exhausted; and the discolored matter has been bleached.

5. The method of bleaching cotton of low grade for color to a per cent reflectance of at least 88.5 Rd comprising the steps of: immcrsing the cotton in an inactive alkaline bleaching solution of a per compound for a minimum period of time of at least 1% to 11/2 hours, maintaining the temperature during a said period of time of at least 1% hours within the range of from 15 C. to not substantially above 50 C., and maintaining the temperature during a said period of time of at least 11/2 hours not substantially above 55 C.; the amount of decomposition of the per compound over the temperature range of C. to about 55 C. while the cotton is immersed in the inactive alkaline bleaching solution for a period of time of not longer than about two hours being not greater than about twenty-six per cent; elevating the temperature of the bleaching solution to about 85 C., whereby the bleaching solution is activated; and maintaining the bleaching solution in an activated state until the per compound is substantially completely exhausted.

6. The method of bleaching cotton of low grade for color; due to the presence of discolored matter within the lumina of the fibers, to a per cent reflectance of at least 88.5 Rd comprising the steps of: immersing the cotton in an inactive alkaline bleaching solution of a per compound for a minimum period of time of at least 11/4 to 11/2 hours, maintaining the temperature during a said period of time of at least 11A; hours within the range of from 15 C. to not substantially above 50 C., and maintaining the temperature during a said period of time of at least 11/2 hours not substantially above 55 C.; the amount of decomposition of the per compound over the temperature range of 15 C. to about 55 C. while the cotton is immersed in the inactive alkaline bleaching solution for a period of time of not longer than about two hours being not greater than about twenty-six per cent; elevating the temperature of the bleaching solution to about 85" C., whereby the bleaching solution is activated; and maintaining the bleaching solution in an activated state until the per compound is substantially completely exhausted and the discolored matter has been bleached.

7. The method according to claim 6 in which the per compound is hydrogen peroxide.

8. The method according toclaim 6 in which the per compound is sodium perborate.

9. The method of bleaching cotton of low grade for color to a per cent reflectance of at least 88.5 Rd comprising the steps of: immersing the cotton in an inactive alkaline bleaching solution of a per compound selected" from the class consisting of hydrogen peroxide, alkali metal peroxides, and inorganic per compounds which behave in aqueous solution as peroxides for a minimum period of time of at least 11A to 11/2 hours, maintaining the temperature during a said period of time of at least 11A hours within the range of from 15 C. to not substantially above 50 C., and during a said period of time of at least 11/2 hours maintaining the temperature not substantially above 55 C.; the amount of decomposition of the per compound over the temperature range of 15 C. to about 55 C. while the cotton is immersed in the inactive alkaline bleaching solution for a period of time of not longer than about two hours being not greater ythan about twenty-six per cent; elevating the temperature of the bleaching solution to about 85 C., whereby the bleaching solution is activated; and maintaining the bleaching solution in an activated state until the per compound is substantially completely exhausted.

l0. A method according to claim 9 in which the per compound is hydrogen peroxide.

11. A method according to claim 9 in which the per compound is sodium perborate.

12. The method of bleaching cotton of low grade for color; due to the presence of discolored matter within the lumina of the fibers, to a per cent reflectance of at least 88.5 Rd comprising the steps of: immersing the cotton in an inactive alkaline bleaching solution of a per compound selected from the class consisting of hydrogen peroxide, alkali metal peroxides, and inorganic per compounds which behave in aqueous solution as peroxides for a minimum period of time of at least 11A to 11/2 hours, maintaining the temperature during a said period of time of at least 1% hours within the range of from 15 C. to not substantially above C., and during a said period of time of at least 11/2 hours maintaining the temperature not substantially above C.; the amount of decomposition of the per com-pound over'the temperature range of 15 C. to about 55 C. while the cotton is immersed in the inactive alkaline bleaching solution for a period of time of not longer than about two hours being not greater than about twenty-six per cent; elevating the temperature of the bleaching solution to about C., whereby the bleaching solution is activated; and maintaining the bleaching solution in an activated state until the per compound is substantially completely exhausted and the discolored matter has been bleached.

13. A method according to claim 12 in which the per compound is hydrogen peroxide.

14. A method according to claim 12 in which the per compound is sodium perborate.

References Cited in the file of this patent UNITED STATES PATENTS 1,278,389 Schaidhauf Sept. 10, 1918 2,220,682 Kautmann Nov. 5, 1940 2,530,244 Jensen Nov. 14, 1950 FOREIGN PATENTS 637,140 Great Britain May l0, 1950 507,759 Germany Sept. 22, 1930 

1. THE METHOD OF BLEACHING COTTON OF LOW GRADE FOR COLOR TO A PER CENT REFLECTANCE OF AT LEAST 88.5RD COMPRISING THE STEPS OF: IMMERSING THE COTTON IN AN INACTIVE ALKALINE BLEACHING SOLUTION OF A PER COMPOUND FOR A MINIMUM PERIOD OF TIME OF AT LEAST 1 1/4 TO 1 1/2 HOURS, MAINTAINING THE TEMPERATURE DURING A SAID PERIOD OF TIME OF AT LEAST 1 1/4 HOURS NOT SUBSTANTIALLY ABOVE 50* C., AND DURING A SAID PERIOD OF TIME OF AT LEAST 1 1/2 HOURS NOT SUBSTANTIALLY ABOVE 55* C., THE AMOUNT OF DECOMPOSITION OF THE PER COMPOUND WHILE THE COTTON IS IMMERSED IN THE INACTIVE ALKALINE BLEACHING SOLUTION FOR A PERIOD OF TIME OF NOT LONGER THAN ABOUT TWO HOURS BEING NOT GREATERTHAN ABOUT TWENTY-SIX PER CENT; ELEVATING THE TEMPERATURE OF THE BLEACHING SOLUTION TO ABOUT 85* C., WHEREBY THE BLEACHING SOLUTION IS ACTIVATED; AND MAINTAINING THE BLEACHING SOLUTION IN AN ACTIVATED STATE UNTIL THE PER COMPOUND IS SUBSTANTIALLY COMPLETELY EXHAUSTED. 